This application claims benefit of Australian Patent Application No. PR3 179, filed Feb. 16, 2001, and titled xe2x80x9cElectro-Acoustic Converter,xe2x80x9d the contents of which are incorporated by reference herein in its entirety.
The present invention relates generally to loud speakers and like devices for converting variations of electrical energy into corresponding variations of acoustic energy, such as, sound. The present invention is suitable for use both in specialized loud speakers forming part of hi-fidelity sound reproduction systems, and as a loud speaker for general applications in televisions, radio and other consumer markets, and it will be convenient to describe the invention in relation to such an exemplary, non limiting applications.
The basic operation of loud speakers and like electro-acoustic converters is well known. In such devices, an electrically driven vibration inducing member, such as a moving coil or piezo-electric crystal, is attached to one end of a diaphragm. Variations in the electrical signal applied to the vibration inducing member are converted into mechanical vibrations which are amplified by the diaphragm and result in the production of sound waves in the air.
In dynamic or moving-coil loud speakers the vibration inducing member includes a moving coil, attached to the diaphragm, which oscillates in an annular cavity of either a specially shaped permanent magnet or an electro magnet. The efficiency of such a loud speaker in converting electrical energy into sound energy is governed by three main factors, namely, the product of the active links of the moving coil and the magnetic field strength, the effective area of the diaphragm, and the total moving mass of the diaphragm, moving coil assembly and the acoustic air load. An increase in the first two parameters, either singly or together will result in an increase in the efficiency of the loud speaker. However, an increase in the mass will result in a reduction in the loud speaker efficiency.
All loud speakers are carefully designed in an attempt to optimize these parameters, based on the specific market the loud speaker is intended for and the manufacturing cost of the loud speaker. However, difficulties arise in the optimization of these parameter. For example, whilst an increase in the area of the diaphragm can often provide the most effective loud speaker gain improvement, high frequency beaming and roll off is found to occur once the area of conventional dome type diaphragms is increased beyond a certain point.
An object of the present invention is to ameliorate or overcome one or more disadvantages of known electro-acoustic converters.
With this in mind, the present invention provides an electro-acoustic converter, comprising a barrel shaped diaphragm formed about a longitudinal axis and comprising first and second annular opposed ends, and a first electrically driven vibration generator for inducing a vibrational movement in the first annular end in the direction of the longitudinal axis.
An electro-acoustic converter having these features enables a greater area of diaphragm to be used in the reproduction of sound waves than do existing electro-acoustic converters, without the high frequency limitations of such standard converters.
Preferably, the electro-acoustic converter comprises a second electrically driven vibration generator for inducing a vibrational movement in the second annular end of the diaphragm in the direction of the longitudinal axis.
The first and second vibration generators may act simultaneously to the first and second annular ends to either compress or stretch the diaphragm.
One or both the first and second vibration generators may be a moving coil drive system. Such a drive system may comprise a vibration coil attached around either or both of the first and second annular ends of the diaphragm.
Alternatively, one or both of the first and second vibration generators may be a crystal drive system. Such a system may comprise a piezo-electric crystal attached to one or both of the first and second annular ends.
A series of electro-acoustic converters according to the present invention, each adapted for the optimal reproduction of a preselected frequency range, may be mounted in a single loud speaker arrangement. For example, the electro-acoustic converters may be arranged in a stack, or in end to end relation. Such an arrangement has been found to optimize the omni-directional sound dispersal of such a loud speaker arrangement.